1. Field of the Invention
The present invention relates to an optical unit including a lens optical system (variable magnification optical system or the like), and to an image taking apparatus provided with this optical unit.
2. Description of the Prior Art
In recent years, following widespread use of personal computers, digital cameras (image taking apparatuses) capable of easily taking in an image have been widespread. Thus, as is the case with cameras using a silver halide film (silver halide film cameras), there has been a demand imposed on such digital cameras for downsizing and performance enhancement (for example, high magnification variation function and high aberration correction function).
For example, image taking apparatuses (digital cameras or the like) as shown in patent publications 1 and 2 below have an zooming optical system (variable magnification optical system) including a plurality of lens units with optical power arrangement of positive, negative, positive, and positive as viewed from the object side toward the image side, and is capable of performing photographing from the wide-angle end position to the telephoto end position.                [Patent publication 1] JP-A-2002-107622 (see claim 1 and the like)                    Disclosure date: Apr. 10, 2002                        [Patent publication 2] JP-A-2001-117000 (see FIG. 5 and the like)                    Disclosure date: Apr. 27, 2001                        
However, these image taking apparatuses capable of zooming suffer from problems below.
The image taking apparatus disclosed in the patent publication 1 performs zooming while a first lens unit (lens unit closest to the object side) is immobilized. Thus, this raises the need for receiving light of a relatively wide angle of view in zooming (in photographing at the wide-angle end position in particular), which leads to a problem of an upsized diameter of a lens element included in the first lens unit (front lens or the like). Therefore, such an image taking apparatus fails to satisfy recent demand for downsizing imposed on an image taking apparatus.
The image taking apparatus disclosed in the patent publication 2, different from the image taking apparatus disclosed in the patent publication 1, performs zooming while the first lens unit is movable. Thus, the diameter of the front lens element is relatively downsized. However, this image taking apparatus disclosed in the patent publication 2 assumes a zooming ratio of approximately 3×, thus failing to satisfy recent demand for function enhancement imposed on the image taking apparatus.
In addition to the problems described above, an image sensor mounted in the image taking apparatus provides higher performance in various points including the number of pixels. Thus, not only compactness and high magnification variation but also high aberration correction function has been increasingly demanded in the photographing optical system.